Recent legislation provides the US Food and Drug Administration (FDA) with regulatory authority over tobacco, including the selection of pictorial imagery for new health warning labels (HWLs) that will cover 50% of the front and back of cigarette packs starting in 2012. US HWL policy is aligned with research that has clearly demonstrated that the most effective HWLs are prominent, cover the front and back of the pack, and include imagery that depicts the consequences of smoking. However, the effects of pictorial HWLs wear out, and the specific characteristics of pictorial HWLs that promote a sustained impact have not been carefully studied. Between-country variation in key characteristics of pictorial HWL policies allows for a natural experiment to determine their relative impact over time. We propose to conduct quasi-experimental and experimental studies among adult smokers in four countries with pictorial HWL policies that differ along key dimensions and that involve implementation of new pictorial HWL content and design in 2012: 1. The US will introduce pictorial HWLs for the first time; 2. Canada will change pictorial HWLs for the first tim after the longest period of exposure in the world (i.e., 11 years); 3. Mexico will continue rotatin new HWLs at the highest frequency in the world (i.e., every three months); and 4. Australia will change its pictorial HWLs while simultaneously implementing the innovative policy of prohibiting brand imagery on cigarette packs (i.e., plain packaging). This project would capitalize on the unprecedented opportunity to systematically examine the over-time effects of changes to HWL policies in four countries that will introduce novel pictorial HWLs in the same year. We will do this by pursuing the following specific aims: Specific Aim 1: We will use a quasi-experimental design with rolling panels of adult smokers in these four countries, in order to determine whether pictorial HWL characteristics that are easiest to process have a more sustained impact on smoking cessation-related cognitions, affect and behaviors than HWL characteristics that require greater cognitive effort to process. Specific Aim 2: We will conduct a series of controlled randomized experiments among adult smokers in the same four countries, systematically varying their exposure to pictorial HWL content and design that is novel relative to existing HWLs, in order to determine the cognitive and affective impact of these manipulations. This project brings together the world's leading experts on tobacco HWL policy to extend the foundation for evidence-based policy development, so that it encompasses the effectiveness and sustainability of different HWL policy options. Results will be disseminated to key decision-makers around the world, including the US FDA and the US Secretary of Health and Human Services, who have the authority to revise HWLs to ensure adequate public understanding of the harms of tobacco use.